Monitoring facility



Sept. 30, 1941. E. J. sHoR'r-r MONITORING `FACILITY INVENTOR EARL d. .sHom- ATTORNEY Patented Sept. 30, i941 MONTORING FACILITY Earl J. Shortt, West Brighton, N. Y., assignor to International Projector Corporation, New York, N. Y., a corporation of Delaware Application March 16, 1940, Serial No. 324,275

8 Claims.

The present invention relates to monitoring facilities for signal reproducing systems.

It is customary in signal reproducing systems and particularly in sound reproducing systems to provide the operating personnel with some form of monitoring facilities. The earlier arrangements of such monitoring facilities consisted of a small loud speaker unit connected in series with a rheostat, or other means of variable control, across the amplifier output. Such speakers absorbed a substantial amount of power. Furthermore, the changing of the monitor control, i. e. the rheostat or other means of control, resulted not only in changing the amplitude of the signal delivered to the auditorium but also substantially affected its frequency characteristic.

Later arrangements introduced separate monitor ampliers between the monitor loud speaker and the output of the system amplifier. These later arrangements absorbed but little power and changing of the monitor control in these later arrangements resulted in negligible changes in the amplitude and the frequency characteristics of the signal delivered to the auditorium. However, failure of any part of the monitor amplier left the operating personnel without any indication of the sound reproducing systems operation.

A feature of the present invention is the prol vision of means for readily removing the monitor ampliers from the circuit and connecting the monitor loud speaker across the sound reproducing system output with a satisfactory control device so as to provide monitoring facilities even if the monitor amplifier becomes defective. In certain systems, for instance, public address systems, it is extremely important that some form .of monitoring facilities be always available and the present invention provides for this.

Other and further features and advantages of the present invention will be apparent from the following description and the drawing in connection therewith in which the figure is a schematic diagram of a sound reproducing system and monitoring facilities embodying the present invention.

Referring now to the figure, I have illustrated a sound reproducing system, such as that employed in theatres, and a monitoring arrangement associated with this system. The arrangement of the sound reproducing systemis standard and is comprised of a sound head unit I0, the usual preliminary amplifier unit II, main amplifier unit I2, divider network I3 for the speaker system, low frequency speaker I4 and high frequency speaker I5. A power supply unit I6 may be provided with the sound reproducing equipment and may also be utilized to supply power for the monitor amplifier.

Associated With the sound reproducing equipment is a monitor network and amplifier unit I'l and a monitor speaker I8. The output of the sound reproducing system or of the main amplier I2 may be connected to the input terminals I9 and 20 of monitor unit II, terminal 20 preferably being the ground side of the system. Terminal I9 is connected through a rheostat 2|, or other variable control to arm 22 of the double pole double throw switch 23. The other arm 24 of switch 23 is connected to one side 25 of the primary 26 of a speaker-matching transformer 2l, the other side 28 of primary 26 being connected directly to terminal 2U. One pole 29 of switch 23 is connected to one side of primary 3|) of a push-pull input transformer 3|, the other side of the primary 3|] being connected to ground or terminal 2D. The secondary 32 of transformer 3| has its ends connected to grids 33 and 34 of a push pull thermionic tube 35.

The center tap 36 of the secondary 32 of transformer 3| is connected to the cathodes 3l and 38 of tube 35. The filament 39 which indirectly heats the cathodes is connected in the usual manner, not shown, to terminals 4D and 4| which are in turn connected to the power supply unit I6. The plates 42 and 43 of tube 35 are connected to the ends of the primary 44 of a pushpull output transformer 45. The center tap 46 f of primary 44 is connected to terminal 4l, terminal 4'I in turn being connected to the power supply unit I6 which provides a source of positive potential for the plates of tube 35, the negative side of said source of potential being connected to ground and through the ground connections to the cathodes of tube 35. The secondary 48 of transformer 45 has one end thereof connected to ground and the other end thereof connected to pole 49 which is adjacent pole 29 of switch 22. The polesl 5D and 5| of switch 22, which are opposite poles 23 and 49, are connected together.

It will be seen that when the arms of the switch 23 are moved to the right as viewed in the figure that signal current from the main amplifiers will pass through the rheostat 2| and through the push-pull input transformer 3|, and will then be amplified in tube 35, the signal output from tube 35 passing through push-pull output transformer 45 and again back through switch 23 to the priformer 45 will be disconnected from the monitor speaker unit I8. When the switch arms are arranged to the left, terminal I9 will be connected through rheostat 2| directly to one end-25 of the transformer 21 and inasmuch as the ground is already connected to end 28 of the primary 2B of transformer 21, signal energy will bedirectly delivered to the speaker 53 and the amplifier unit will be completely cut out.

It is to be noted that the amplifier arrangement, illustrated and described, is of a pushpull variety and it will be apparent that such an amplifier will tend to cancel noises arising within the amplifier so that such a unit will can'- cel any hums emanating fromthe power supply unit as well as stray interferences picked up in the amplifier circuit itself.

It win be apparent that when the monitor amplifier is inserted between the output of the main amplifier and the monitor speaker, varying rheostat 2| will have a negligible eifect on the amplitude and frequency characteristics of the signal delivered'to the speakers I4 and I5 of the sound reproducing system. On the other hand, when the monitor speaker unit I8 is connected directly through rheostat 2| to the output of the main amplifier unit I2 variation of the rheostat 2| will have a definite effect upon both the amplitude and the frequency characteristics of the signal output to the speakers |l| and I5 of the sound reproducing system. However, the latter arrangement will provide adequate monitoring facilities for emergency purposes.

It will be seen that I have provided facilities which are normally adapted not to affect the signal output of the sound reproducing system and that can, upon failure of the monitor amplifier, be arranged to operate in such. emergencies to provide monitoring facilities.

While I have described the monitoring facilities of the present invention as being associated with 'a sound reproducing system such vas is employed in connection with motion picture projection, it will readily be apparent that these monitoring facilities might be employed with any other type of signal reproducing systems, such as for instance, radio systems or public address systems.

While a preferred embodiment of my invention has been described, it is to be understood that this description is not a limitation upon the scope of the invention, which is to be determined only by the appended claims.

I claim:

1. The combination with a sound reproducing system of a monitor speaker, a monitor amplifying unit, a rheostat, the output of the sound reproducing system being connected in series with the rheostat to the input 'of the monitor-amplifying unit, the output of the monitor amplifying unit being connected to the monitor speaker and a switch having a plurality of arms, said switch arranged intermediate the outputiof th'esound reproducing system and the input of 'the monitor gesamt amplifying unit and between the output of the monitor amplifying unit and the speaker, one of the arms of said switch being connected in series with the rheostat to the output of the sound reproducing system, another of said arms being connected to the monitor speaker, said arms being adapted upon operation of the switch to connect the output of the sound reproducing system to the speaker and substantially simultaneously to disconnect the monitor amplifying unit from the sound reproducing system and the monitor speaker.

2. 'Ihe combination with a sound reproducing system of a monitor speaker, a monitor` amplifying unit, a rheostat, the output of the sound reproducing system being connected in series with the rheostat to the input of the monitor amplifying unit, the output of the monitor amplifying unit being connected to the monitor speaker and a switch arranged in the circuit adapted to substantially simultaneously disconnect the monitor amplifying unit from the output of the sound reproducing system and to connect the monitor speaker in series with the rheostat to the output of the sound reproducing system.

3. The combination with a sound reproducing system, of a monitor speaker and a monitor amplifying unit, the output of the sound reproducing system being connected to the input of the monitor amplifying unit, the output of the monitor amplifying unit being connected to the monitor speaker and a `switch arranged in the circuit and adapted to substantially simultaneously disconnect the monitor amplifying unit from the circuit and connect the monitor speaker directly to the output of the sound reproducing system.

4. The combination with a sound reproducing system, of a monitor speaker and a monitor amplifying unit, the output of the sound reproducing system being connected -to the input of the monitor ramplifying unit, the output of the monitor amplifying unit being connected to the monitor speaker and a switch having a plurality of arms, one of said arms arranged intermediate the output of the sound reproducing system and the input of the monitor amplifying unit, another of said arms arranged intermediate the output of the monitor amplifying unit andthe speaker, said arms being adapted upon operation of the switch to connect the output of the sound reproducing system directly to the speaker.

5. In the method of monitoring a sound reproducing system the steps of shunting a portion. of the signal current output of the sound reproducing system to an amplifier, amplifying the shimted current and translating the amplified shunted current into sound signals and the steps oi switching the amplifier out of the circuit and translating the shunt-ed current from the sound reproducing system without further ampliiication into sound signals.

6. In the method of monitoring a sound reproducing system the steps of shunting a portion of the ysignal current output of the sound reproducing system to an amplifier, controlling the amount of current shunted, amplifying the shunted current and translating the amplified shunted current into sound signals and the steps of switching the amplier out of the circuit and translating the shunted current from the sound reproducing system without further amplification into sound signals.

1. The combination with a sound reproducing system of `a monitorspeaker, a monitor push pull amplifier, theoutput of the sound reproducing system being connected to the input of the monitor push pull amplifier, the output of the monitor push pull amplifier being connected to the monitor speaker and means for substantially simultaneously disconnecting the monitor push pull amplifier from the output of the sound reproducing system and the monitor speaker and connecting the monitor speaker to the output of the sound reproducing system.

8. The combination with a sound reproducing system of a monitor speaker, a monitor amplifying unit, a rheostat, the output of the sound reproducing system being connected in series with the rheostat to the input of the monitor amplifying unit, the output of the monitor amplifying unit being connected to the monitor speaker and a switch arranged in the circuit adapted to substantially simultaneously disconnect the monitor amplifying unit from the monitor speaker and to connect the monitor speaker in series with the rheostat to the output of the 10 sound reproducing system.

EARL J. SHORTT. 

